document12

PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

12

The Central Nervous System: Part D


The Spinal Cord: Embryonic Development

• By week 6, there are two clusters of neuroblasts• Alar plate—will become interneurons; axons

form white matter of cord• Basal plate—will become motor neurons;

axons will grow to effectors• Neural crest cells form the dorsal root ganglia

sensory neurons; axons grow into the dorsal aspect of the cord

Copyright © 2010 Pearson Education, Inc. Figure 12.28

Whitematter

Neural tubecells

Centralcavity

Alar plate:interneurons

Dorsal root ganglion: sensoryneurons from neural crest

Basal plate:motor neurons


Spinal Cord

• Location• Begins at the foramen magnum

• Ends as conus medullaris at L1 vertebra

• Functions• Provides two-way communication to and from

the brain

• Contains spinal reflex centers


Spinal Cord: Protection

• Bone, meninges, and CSF

• Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater

• CSF in subarachnoid space


Spinal Cord: Protection

• Denticulate ligaments: extensions of pia mater that secure cord to dura mater

• Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx


Ligamentumflavum

Supra-spinousligament

Lumbar punctureneedle enteringsubarachnoidspace

Filumterminale

Inter-vertebraldisc

T12

L5

Cauda equinain subarachnoidspace

Duramater

L5

L4

S1

Arachnoidmatter

Copyright © 2010 Pearson Education, Inc. Figure 12.29a

Cervicalenlargement

Dura andarachnoidmater

LumbarenlargementConusmedullarisCaudaequinaFilumterminale

Cervicalspinal nerves

Lumbarspinal nerves

Sacralspinal nerves

Thoracicspinal nerves

(a) The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.


Spinal Cord

• Spinal nerves• 31 pairs

• Cervical and lumbar enlargements• The nerves serving the upper and lower limbs

emerge here

• Cauda equina• The collection of nerve roots at the inferior end

of the vertebral canal


Cross-Sectional Anatomy

• Two lengthwise grooves divide cord into right and left halves • Ventral (anterior) median fissure

• Dorsal (posterior) median sulcus

• Gray commissure—connects masses of gray matter; encloses central canal

Copyright © 2010 Pearson Education, Inc. Figure 12.31a

(a) Cross section of spinal cord and vertebra

Epidural space(contains fat)

Pia materSpinalmeninges

Arachnoidmater Dura mater

Bone ofvertebra

Subdural spaceSubarachnoidspace(contains CSF)

Dorsal rootganglion

Bodyof vertebra

Copyright © 2010 Pearson Education, Inc. Figure 12.31b

(b) The spinal cord and its meningeal coverings

Dorsal funiculus

Dorsal median sulcus

Central canal

Ventral medianfissure

Pia materArachnoid mater

Spinal dura mater

Graycommissure Dorsal horn Gray

matterLateral hornVentral horn

Ventral funiculusLateral funiculus

Whitecolumns

Dorsal rootganglion

Dorsal root(fans out into dorsal rootlets)

Ventral root(derived from severalventral rootlets)

Spinal nerve


Gray Matter

• Dorsal horns—interneurons that receive somatic and visceral sensory input

• Ventral horns—somatic motor neurons whose axons exit the cord via ventral roots

• Lateral horns (only in thoracic and lumbar regions) –sympathetic neurons

• Dorsal root (spinal) gangia—contain cell bodies of sensory neurons


Somaticsensoryneuron

Dorsal root (sensory)

Dorsal root ganglion

Visceralsensory neuron

Somaticmotor neuron

Spinal nerve

Ventral root(motor)

Ventral horn(motor neurons)

Dorsal horn (interneurons)

Visceralmotorneuron

Interneurons receiving input from somatic sensory neurons

Interneurons receiving input from visceral sensory neurons

Visceral motor (autonomic) neurons

Somatic motor neurons


White Matter

• Consists mostly of ascending (sensory) and descending (motor) tracts• Transverse tracts (commissural fibers) cross

from one side to the other• Tracts are located in three white columns

(funiculi on each side—dorsal (posterior), lateral, and ventral (anterior)• Each spinal tract is composed of axons with

similar functions


Pathway Generalizations

• Pathways decussate (cross over)

• Most consist of two or three neurons (a relay)

• Most exhibit somatotopy (precise spatial relationships)

• Pathways are paired symmetrically (one on each side of the spinal cord or brain)


Ascending tracts Descending tractsFasciculus gracilisDorsal

whitecolumn

Fasciculus cuneatus

Dorsalspinocerebellar tract

Lateralspinothalamic tract Ventral spinothalamictract

Ventral whitecommissure

Lateralcorticospinal tract

Lateralreticulospinal tract

Ventral corticospinaltract

Medialreticulospinal tract

Rubrospinaltract

Vestibulospinal tractTectospinal tract

Ventralspinocerebellartract


Ascending Pathways

• Consist of three neurons

• First-order neuron• Conducts impulses from cutaneous receptors

and proprioceptors

• Branches diffusely as it enters the spinal cord or medulla

• Synapses with second-order neuron


Ascending Pathways

• Second-order neuron• Interneuron

• Cell body in dorsal horn of spinal cord or medullary nuclei

• Axons extend to thalamus or cerebellum


Ascending Pathways

• Third-order neuron• Interneuron

• Cell body in thalamus

• Axon extends to somatosensory cortex


Ascending Pathways

• Two pathways transmit somatosensory information to the sensory cortex via the thalamus• Dorsal column-medial lemniscal pathways

• Spinothalamic pathways

• Spinocerebellar tracts terminate in the cerebellum

document12

Documents

pearson education

spinal cordlocationbegins

cross section of spinal

spinal dura mater csf

secure cord

dorsal rootletsventral

dorsal aspect

dura materfilum terminale